Isshin needs to arrive, hopefully soon.
Blackbeard getting two is a plot point. It's supposed to be a mystery that's the entire point of it. And they always have an explanation for the power ups, Luffy used his rubber to blood dope himself and inflate his bones, Haki is a universal thing. Name one of the unexplained power boosts.
Waiting for an explanation is not an excuse. After 16 years we still don't know much about devil fruit and that is one of the big pillars of the manga, and not explaining it after all this time is really bad writing. Gears is only explained by that Luffy saw sour and copied it. We did not see how Luffy thought of it. Not to mention every asspull Zorro and Sanji's pulled in their fights. Zora pulled that Asura thing out of the ass against Zebra guy of CP9. And Sanji's flaming leg came out of no where. Not to mention Oda's inconsistency in writing good women characters in the manga.
Blackbeard eating two fruits is something that simply hasn't been explained yet and there are even a few interesting theories as to why he was able to eat two fruits. There's a reason the other characters were surprised when he did it. It's not something that's supposed to happen. Oda has shown that he thinks ahead at least for the most part. Kubo seems to get stuff out of his ass. I think this arc actually started out really good, but ever since Yamamoto died, it's been downhill save the part where Ichigo and the others start recovering with Squad Zero. I even went back and re-read the arc from the beginning to see if the problem was with how short the chapters were but that didn't help. The fights just haven't been very exciting and the writing is just awful.
Wait for the explanation is a bad excuse for crappy writing.
Kubo did not pull anything out of the ass. It's all being explained. Juha Bach vs. Ichibei is an amazing fight, Yamamoto, Masculine, Byakuya getting by his fear. Plenty of enjoyable fights. There were some bad fights like Hitsugaya vs. Kang Du. Fyi you not liking something does not mean it's bad writing.
That's really off topic so .....